1. Field of the Invention
The present invention relates to a sounding-body driving circuit outputting to a sounding body a drive signal for generating an artificial striking sound similar to a striking sound of a mechanical relay, and to an operating-sound generating apparatus using the circuit.
2. Description of the Related Art
A direction indicating apparatus of a vehicle generally has a mechanical relay for flashing a turn signal indicator, which is flashed by the mechanical relay in accordance with operation of a turn signal lever. Further, a driver of the vehicle can recognize that the turn signal indicator is in a state of flashing by means of both a visual warning of the flashing display of the indicator and an audio warning of the striking sound of the mechanical relay.
The mechanical relay is generally disposed near the driver""s seat so that the driver can hear the string sound. In the case where the mechanical relay is miniaturized, or disposed in the engine room for circuit construction reasons, it becomes hard for the driver to hear the striking sound of the mechanical relay. Furthermore, when the flashing operation of the turn signal indicator is performed using a semiconductor switch and the like, the mechanical relay itself is unnecessary, so that the striking sound of the mechanical relay is not generated.
On the other hand, as disclosed in Japanese Unexamined Utility Model Publications JP-U 59-102448(1984) and JP-U 4-136948(1992), in the case of adopting such a construction that a sounding body such as a piezoelectric buzzer or a speaker is used and driven to generate a sound synchronized with the flashing operation of the turn signal indicator, the flashing operation state of the turn signal indicator can be indicated auditorially to the driver without the striking sound of the mechanical relay.
However, since the striking sound of the mechanical relay has been used for a long time as a flashing operation sound of the turn signal indicator, drivers are accustomed to such a tone. Accordingly, in the case where a sound different from a striking sound is generated as a flashing operation sound from the sounding body, as disclosed in the publications, the drivers have an undesireable unusual feeling because the flashing operation sound is fairly different in tone from the accustomed striking sound of the mechanical relay.
In the case of reproducing the striking sound of the mechanical relay faithfully, as shown in FIG. 9, it is necessary to generate a driving signal having an irregular waveform 4 showing a complicated envelop 2. There is consequently a problem such that the driving circuit is complicated and expensive.
It is an object of the invention to provide a sounding-body driving circuit and operation sound generating apparatus which allows generation of a flashing operation sound of a turn signal indicator with a simple and low-cost construction without presenting an unusual feeling to a vehicle driver.
Even if the striking sound of a mechanical relay is not reproduced faithfully, when an artificial striking sound similar to the striking sound is obtained as the flashing operation sound of the turn signal indicator, the driver has no unusual feeling toward the artificial striking sound. Thus, the object of the invention is achieved by adopting a driving circuit for generating the artificial string sound and putting some constructional thought into designing the driving circuit.
According to the invention, there is provided a sounding-body driving circuit outputting to a sounding body a driving signal for generating an artificial string sound similar to a striking sound of a mechanical relay. The sounding-body driving circuit generates a plurality of signals having different frequencies, synthesizes the plurality of signals in sequence of time, and repeatedly outputs the generated synthetic signal at intervals of a predetermined time.
No restriction is placed on the plurality of signals with respect to frequency, waveform, amplitude etc. as long as they are different in frequency. For example, with respect to waveform, any wave such as a rectangular wave, sine wave, triangular wave or the like may be used. With respect to amplitude, a constant value may be set or different values may be set at random or according to differences in frequency between the signals.
There is no particular restriction on the specific method of synthesizing the plurality of signals in sequence of time (e.g., order of synthesis of the signals, wave number of each signal, or method of combining the signals).
The synthetic signal denotes a signal obtained by connecting in sequence of time at least two kinds of signals of different frequencies. A synthetic signal may be generated by forming two or more kinds of signals of frequencies by a single oscillation circuit and connecting the signals in sequence of time.
As shown in the construction mentioned above, the sounding-body driving circuit according to the invention outputs the driving signal for generating an artificial striking signal to the sounding body. Since the plurality of signals having different frequencies are generated and synthesized in sequence of time and the synthetic signal thus generated is repeatedly outputted at intervals of a predetermined time, the following effects can be obtained.
Various tones can be obtained by synthesizing a plurality of signals having different frequencies, such various tones cannot be obtained by signals of a single frequency. The synthesis is performed in sequence of time so that the plurality of signals are properly arranged to generate a synthetic signal and the synthetic signal is outputted to the sounding body, thereby realizing an artificial string sound similar to the striking sound of the mechanical relay. Moreover, since the synthetic signal is repeatedly outputted at intervals of a predetermined time, by adjusting the predetermined time to a proper value, not only the tone of the artificial striking sound but also the generation interval can be made similar to those of the flashing operation sound of the turn signal indicator, that is, the striking sound of the mechanical relay.
According to the invention, a plurality of signals having different frequencies are generated and synthesized in sequence of time (that is, simply connected based time), thereby realizing an artificial striking sound similar to the striking sound of the mechanical relay with a simple and low-cost construction. By repeatedly outputting the synthetic signal at intervals of a predetermined time, the flashing operation sound of a turn signal indicator which does not sound unusual to the driver can be obtained.
Although there is no specific restriction on the duration of the synthetic signal of the invention, since the duration of the striking sound of the mechanical relay is about 12 ms, it is preferable to set the duration to 12 ms or less, more preferably 6 ms or less. It is generally said in connection with the sense of hearing of humans that a duration of 1 ms or more is necessary to identify the tone of the sound, a duration of 10 ms or more to have sequential feeling, and a duration of 100 ms or more to perceive the order of time. When the duration of the synthetic signal is set to be longer than required, the sound becomes similar to an electronic sound rather than similar to the striking sound of the mechanical relay. It is preferable to set the duration of the synthetic signal rather short to such an extent that the sequential feeling of the sound is not perceived.
As long as the sounding-body driving circuit is constructed to generate a plurality of signals having different frequencies, to synthesize the plurality of signals in sequence of time, and to repeatedly output the generated synthetic signal at intervals of a predetermined time, the signal process may be performed in a software or hardware manner. A specific construction of the latter manner is, for example, a construction comprising a signal generating circuit for generating a plurality of signals having different frequencies, a signal synthesizing circuit for synthesizing the plurality of signals generated by the signal generating circuit in sequence of time, and a synthetic signal output circuit for repeatedly outputting the synthetic signals generated by the signal synthesizing circuit at intervals of a predetermined time.
In the construction mentioned above, by generating two kinds of synthetic signals and alternately outputting them, the following effects can be obtained.
In general there are two kinds of striking sounds of the mechanical relay. One striking sound generates when the movable piece of the mechanical relay comes into contact with the iron core and the other striking sound generates when the movable piece comes into contact with a contact point. The two kinds of striking sounds are alternately generated to make the flashing operation sound of the turn signal indicator of a vehicle. It is therefore preferable to make the artificial sounds similar to the two kinds of striking sounds. When the two kinds of synthetic signals are generated and alternately outputted, an artificial striking sound can be generated at the tone similar to the flashing operation sound which is an actual striking sound of the mechanical relay.
In this case, as long as the two kinds of synthetic signals are different from each other, there is no specific restriction on their construction. For example, a plurality of signals constructing the synthetic signal may be different in only any one of frequency component, duration and amplitude or two or three thereof.
Although the sounding-body driving circuit according to the invention has a construction suitable for obtaining the flashing operation sound of a turn signal indicator of a vehicle as mentioned above, there is no restriction on the circuit in respect of use. The circuit can be generally used for the case where it is necessary or preferable to generate an artificial striking sound similar to the striking sound of the mechanical relay.
In a use other than the use of obtaining the flashing operation sound, there may be a case where the synthetic signal does not have to be repeatedly outputted at intervals of a predetermined time. From this point of view, a sufficient technical value can also be found in the construction as the sounding-body driving signal generating circuit for generating a plurality of signals having different frequencies and synthesizing the plurality of signal in sequence of time. That is, the sounding-body driving signal for generating the artificial striking sound similar to the striking sound of the mechanical relay can be obtained by the synthetic signal generated by the sounding-body driving signal generating circuit. Therefore, when the sounding-body driving signal is outputted to the sounding body at proper timing, an artificial striking sound adapted to the generation pattern of the striking sound of the mechanical relay used for various uses can be generated.
On the other hand, when the sounding-body driving circuit according to the invention is constructed as a part of the operating-sound generating apparatus of the turn signal indicator, the synthetic signal is outputted synchronously with the timing of the turn-on and turn-off of the turn signal indicator. The artificial striking sound can be generated at the same timing as the generation timing of the flashing operation sound which is the striking sound of the mechanical relay, so that the possibility of the driver thinking the sound is unusual can be more effectively prevented.
When the sounding-body driving circuit is constructed as a part of the operation sound generating apparatus of the turn signal indicator, by generating two kinds of signals and alternately outputting the two kinds of signals synchronously with the timing of the turn-on and turn-off of the turn signal indicator, a flashing operation sound of the turn signal indicator which does not sound unusual to the driver can be obtained.
By alternately outputting the two kinds of signals, two kinds of artificial striking sounds are alternately generated from the sounding body. Even if each artificial striking sound itself is not similar to the striking sound of the mechanical relay, a synthetic signal obtained by synthesizing a plurality of signals having different frequencies is not used as the driving signal and the generation pattern of the artificial striking sound is the same as that of the flashing operation sound of the turn signal indicator by the striking sound of the mechanical relay. Therefore, the flashing operation sound of the turn signal indicator can be prevented from sounding to the driver. By adopting such a construction, the sounding-body driving circuit can be constructed simpler at lower cost.
In the operation sound generating apparatus of the turn signal indicator having the sounding-body drive circuit and the sounding body, the flashing operation sound of the turn signal indicator which does not sound unusual to the driver can be obtained as mentioned above. Using the sounding body of the operation sound generating apparatus, sounds other than the flashing operation sound can be also generated. That is, by adding proper driving means, the function of warning of a failure in the direction indicating apparatus (for example, burn-out of a bulb in the turn signal indicator), a failure in other apparatuses mounted on the vehicle, and the like can be provided.